This is an interesting thought - and yes, I think it is a bit taboo to admit to controlling your weight during pregnancy.
I think partly it's a matter of vocabulary. Someone who says they're dieting during pregnancy might get a negative response, probably because most people associate a diet with strict calorie control and weight loss. And there are some bonkers diet plans out there which would clearly be unhealthy during pregnancy.
But someone who says they are trying to eat healthily might get a better response. Even if, strictly speaking, they are doing the same thing - selecting food carefully for nutrition and to minimise weight gain, rather than just eating randomly or unhealthily.
That said... there are odd attitudes out there. Out with a couple of mates last week for a coffee, I had the choice between a muffin and a banana, and chose a banana. Because it was healthier and less pointlessly fattening [empty calories]. One friend really put pressure on me to have a muffin, using the old 'eating for 2' line, was very down on the fact that I was thinking about choices at all, and told me 'dieting' was bad for me (let's just remember, I was eating a banana instead of a muffin...hardly the Atkins or cabbage soup diet, eh). She's someone who struggles with her weight a bit, and I just thought - hmm, this isn't about ME or my pregnancy, is it.... I was caught a bit off balance, and I wish I'd had enough presence of mind to say, 'honestly, which do you think is genuinely better for me and my developing baby here??'
I've also had people almost tell me off for not having cravings ("you could eat a whole tub of icecream if you wanted!"). Well, sure, but it's not my job to live out someone else's wish fulfillment, is it?
And I think that's the heart of the problem. Women and our relationships with weight/food can be so bloomin' complicated, pregnancy can be a bit of a lodestone for all sorts of unhelpful attitudes and agendas.
So much of pregnancy is luck of the draw, anyway, and there's no fairness at all in who gets sickness, and who gets cravings etc. I know my life is a lot easier cos I've had neither of the above, and I have noooo smugness or misplaced sense of achievement about that - I'm just very, very grateful.
Ah - nearly forgot - in my local hospital, where you wait for your antenatal scans etc, there's a whole wall given over to advice about dieting during pregnancy for obese women. It actually says 'did you know you CAN lose weight while you're pregnant?' I admit, I was surprised when I saw it - but I've read all the recipes they have up there while I'm waiting, and they're all just v healthy eating. They do specialist recommendations to Weight Watchers, and advocate the 'syns' system. So there you go, that's in a midwifery led unit, so I guess they think it's OK!